An example of an electric power tool, which can carry out a variety of operations including an operation of cutting an object, an operation of polishing an object, and an operation of peeling off an object by transmitting the drive power of an electric motor to a tip tool, is described in Japanese Patent Application Laid-Open Publication No. 2012-232381 (hereinafter simply refer to as “Patent Document 1”). The electric power tool described in Patent Document 1 has: an electric motor provided in a tool main body; an output shaft attached to the tool main body; a drive power converting mechanism provided in the tool main body and configured to convert a rotative force of the electric motor into a swinging force of the output shaft; a tip tool attached to the output shaft; a control part provided in the tool main body and configured to control the rotating speed of the electric motor, a speed changing dial provided in the tool main body and operated by an operator, and a main switch.
In the electric power tool described in Patent Document 1, the operator operates the main switch, so that the electric motor is rotated or stopped. When the rotative force of the electric motor is transmitted to the output shaft via the drive power converting mechanism, the tip tool reciprocates within a range of a predetermined angle, and for example, an operation of cutting an object, an operation of polishing an object, or an operation of peeling off an object is carried out. In the electric power tool described in Patent document 1, the tip tool can be replaced in accordance with the operation to be carried out. Furthermore, when the operator operates the speed changing dial, the rotating speed of the electric motor can be increased or reduced in accordance with the load of the operation, the type of the tip tool, etc.
However, in the electric power tool described in Patent document 1, the operator has to operate the speed changing dial so as to change the rotating speed of the electric motor in accordance with the load of that tip tool, that is, the type of that tip tool and the type of that operation, and it is cumbersome to operate it.
As another example, an electric power tool is also described in Japanese Patent Application Laid-Open Publication No. 2010-162672 (hereinafter simply refer to as “Patent Document 2”).
An object of the present invention is to provide an electric power tool capable of automatically changing the rotating speed of the electric motor in accordance with the load of the tip tool.
Another object of the present invention is to provide a technique capable of detecting the load state of the electric motor with high precision.